Resnatron



July 31., 1956 G. E. sHEPPARD Erm. 2,757,314

RESNATRON Filed Jan. 19, 1951 INVENToRs 6: E //f'pp M @Heal/Ny. BY

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.714:15 rv Inf/l, III', all l I .power `is produced which .famplgiierwith that of fan absorption United Statesr Patent "O RESNATRON Glenn E. Sheppard, Wilkinsburg, land Max Garbuny,

Pittsburgh, Pa., assignors to -Westinghouse Electric Corporation, East Pittsburgh, Pa., -a corporation of Pennsylvania Application January 19, 1951, Serial No. y2il6,f144 2 Claims. (Cl. 315-43) This invention relates to an electronic tube lfor ultra high frequencies and has particular relation to `anelectronic tube of the resnatron type which is essentially a tetrode having two cavity resonators, one for thefgridcathode and the other for the screen-anode space.

A resnatron electronic device as lconstructed in accordance with the prior art, generally arranges the pair of resonators to have electromagnetic iield oscillations kof substantially the same frequency therein and with the resonators positioned adjacent each other with a .cathode mounted within the rst resonator and an anode mounted Within the second resonator. Openings in the adjacent walls of the two resonators permit a flow of electrons from the cathode to the anode. These electrons pass through one or `more grids positioned in the path thereof and it is usual for at least one grid to have appropriate potential applied thereto for modulating or repetitiously interrupting the flow of electrons. In amplifier operation the first resonator is fed by an R. F. driver source or else in oscillator operation the resonators are interconnected by a feedback from the second resonatorto the first so that the electrons are density modulated by the grid operating at a relatively high voltage and enter Ainto the second cavity wherein they find a Vregion `either free of a direct current eld or one which contributes a small accelerating potential.

ln Ithese prior Vart resnatrons, the electrons are emitted from the cathode and are collected bythe anode, vtraversirig a straight line -path from one to the other, the anode, as the terminal, having a positive potential uwith respect to the screen.

We have found that if, under otherwise unchanged conditions, the anode of a prior art resnatron is held at or near the same potential as the cathode potential, again isa multiple of that'i-n the driverstage. ln `each instance, the output powergis a function of the screen gridvoltage, having a maxi/trium for a certain valueof said grid.voltage. lInl-this connection, itpshould be Vnoted that this operation is `different v:from thatof `such devices as the Barkhausen oscillators which employ a negative anodebutemploya single acy celeratingy grid around which the electrons describe many oscillations vfin which` by `a process of self-bunchingafsmall net contribution to ItheR. F. eldis beingfniade.

Accordi-ng tothe present invention, astill further step inadvance is taken to increase the efiiciency andto tover- `come relianceon grid` rmodulation involvingconsuinption e of i. power.

AAn object ofthe invention -is to adapt -aaresnatronto .modulationof the carrier` output withasinall ,requirement ``of power.

`Another object of the invention Iis to adapt faresnatr,on

.to reflex operation.

Another object vof :the invention is toprovide aresnatron which combines the characteristics of ua gpower modulator, and to do`,so,.with-little orinopower demand ontheinodulation .generam- Vsmall accelerating potential.

invention, the

l, is located if Vthey traverse the distance .proximitytogthe reiector during the 2,757,314 Patented July 31, 1956 `.screen grid and anode than heretofore permissible.

Again, an object of the invention is to collect the electrons over a large area and one which is readily and adequately cooled.

Finally, an object of the invention is to provide a resnatron in which detrimental secondary electrons are largely suppressed, not by means of complicated structure, but by the presence of a retarding field itself.

Other objects of the invention will appear to those skilled in the art to which the invention appertains as the description proceeds, both by direct reference thereto and by implication from the context.

.Referring to the accompanying drawing, in which like numerals of reference indicate similar parts throughout the several views:

Fig. l is a longitudinal section of a resnatron constructed in accordance with our invention;

Fig. 2 is a detailed view of a portion of Fig. 1, showing the electrodes on larger scale and indicating the elec- .,tronpaths in general; and

Fig. 3 is a cross-Section on line III-III of Fig. 1.

In its broad aspects, the present yinvention contemplates novelty over the prior art in modulation of the'power output by impressing a negative signal potential on the electrode which, `in the prior art, constituted the-anode of the resnatron instead o'fby use of a grid bias. Ordinarily in resnatrons, the electrons, density modulated oythe grid, are accelerated by a relatively high positive screen grid voltage and enter the anode cavity under that screen grid acceleration and there find a region either f ree of a direc/t current eld or one contributing only a in the prior artmodula non was either impossible or was obtained `only Vwith high driver powers and considerable reduction 'of bandwidth by varying the grid potential. y

We have found, however, that if the cathode and electrode which, in the prior art, constituted the anode `are on the same or nearly the same potential, this potential being highly negative with respect to the screen grid, efficient production of R. F. power is again obtained, but in addition in such a manner that modulation of `the outputis Vadvantageously obtained by impressing the signal on the electrode which, in the prior art, constituted the anode. Experimental observations leading `to and producing the superior l V with the present invention, are supported by theory. In the above-mentioned case of the prior art anode being held at cathode potential it was experimentallyobserved that 4the magnitude `and efficiency of the radio frequency output both approximated the magnitude and eiiiciency of the resnatron when operated normally, and also that the resulting frequency was equal to that of the two cavity resonators of the resnatron. Furthermore, the effective performance noted occurred with amplifier operationand with a screen opening which prevented a majority of electrons from escaping from the anode cavity. The frequency showed no dependence on screen voltage.

Considering these phenomena from a theoretic standpoint, and initially assuming small radio frequency signals, electrons entering the anode cavity are VKdecelerated by the potential of the prior art anode until they come to rest proximate to said prior `art and are then reflected back to the screen grid. Consequently, according to this prior art anode is utilized as a reflector. The electrons yield maximum energy to the radiofrequency fieldof the cavity resonator in which the reflector from the screen to retarding cycle of wherein T is the total transit time of the electron in the screen-to-reflector gap and To is the radio frequency period. [isc is the electron velocity in fractional light speed at moment of initial passage through the screen, and

'is the gap spacing in terms of fractional wavelengths.

Transposed, the above formula becomes 4d sc= The derivation of the above formulas is based on exl perirnentally justified simplifications and on the assumption that the phase of the produced radio frequency voltage adjusts itself to maximum power output (which will always hold as a consequence of Maxwells equations) and that moreover the electrons spend a complete cycle in the reflector gap, which is true up to a certain limit of conversion, efficiency, but suflicient for the conditions here considered. And for present purposes, it is assumed that for the electron transit time traversing gap distance d, the influence of the radio frequency ileld can be neglected, since the signal is assumed to be small, and that the rellector is at cathode potential, or in other words, there is no bias.

Now proceeding to the case of a static or modulating potential on the reflector, negative to that of the cathode by a voltage V1 corresponding to a fractional light speed i of an electron, but still assuming negligible radio frequency field, the electron will be turned back at a zero potential line a distance d1 from the screen grid. This reduces the path length in the ratio of V85 Vsc'i-Vl or equivalent in terms of electron velocity as and for resonance condition the new distance di is less than distance d, but the travel time T for the electron still is equal to the radio frequency period. In other Since the radio frequency conversion elliciency is very sens1t1ve to correct phasing of the arrival of the electrons,

a relatively small variation of V1, the negative reflector potential, and therefore its equivalent velocity change of the electron, i, produces a high degree of modulationl in Aradio frequency output or power.

Results in practice substantiate the theory and vice versa.

It was indicated above that effect of signal voltages was neglected, that being done for simplicity of initial explanation and permissible where signal voltages are low. In case of high signal levels, electrons will not necessarily reverse their course at the moment of radio frequency reversal, but with a phase difference with respect to that time. Here various conditions are possible. If, in accordance with the above description, the reflector is negative to the cathode, and the radio frequency voltage rises to such a value that electrons give practically all of their energy to the radio frequency field, the resonance condition obtained, instead of that given above, is

ac-i' Bec- This equation, as well as those expressions relating to intermediate efllciencies of energy conversion, may be derived, for example, on the basis of an article entitled Graphical Representation of Particle Trajectories in a Moving Reference System in the Journal of Applied Physics, vol. 21, Oct. 1950, pages 1054 to 1056.

The logical reason for the difference by a factor of two in the last two equations given above, is simply that the radio frequency field is, to be useful, also retarding, so that with full signal strength the electrons lose much of their energy in comparison to the case of the negligible signal. The penetration distance is therefore reduced. As a result, for the same gap d the applied voltages of screen and (negative) reflector bias must be smaller, so that a full cycle passes again, although a smaller total distance is travelled.

Those acquainted with the art can easily derive from this latter equation that the electrons penetrate in this instance only a fraction of the reflector-screen gap before turning back, because the kinetic energy of the electrons is efficiently converted into electromagnetic f1eld energy of the cavity. In order to better utilize the available gap space therefore, we prefer to increase the bias of the reflector towards more positive values which will depend on the degree of conversion efficiency achieved.

From the foregoing, it will be understood that a feature of the invention lies in the use of a resnatron as a reflex resnatron and from the facts stated, that a resonance condition is imposed for the efficient operation thereof including imposition of a relation between screen grid and reflector voltages in the basic ratio of according to the correlated equations. It can be shown from these equations that, other things being equal, delinitely greater distances between reflector and screen have to be used than in the prior art conventional resnatron between anode and screen, thus giving the advantage of greater tolerance in manufacture and assembly of the device. Emphasis is also here added of the feature of the invention that the modulation action of the reflector consists in varying the contribution of the electrons to the field of radio frequency energy in the device.

Finally, it is pointed out that the invention provides for effective elimination of secondary electrons. In the anode spaces of the conventional resnatron either no retarding direct current fiel-d is acting at all, or it is rather small so that secondary electrons can interact with the accelerating phase of the radio frequency. To reduce this detrimental influence complicated structures in the anode profile are used therefore. This invention however inhibits to great extent the influence of secondary electrons by providing a high retarding direct current potential.

A particular structure, as shown in the drawing, for achieving the advantageous results outlined above, is herein arbitrarily selected as an example of the inven- -mediu1n, such as water,

tion'. That specific embodiment comprises any envelope in. general, fabricated as ai body of revolution about an axis andi shown as' two metallic outer cylinders o1 body sections 10, arranged endwise toward' each other and upon an axis common to both. The ends facing toward each other of said body sections are held .in proximity to,- but with insulative spacing from. each other, by a glass or other endlessband insulator 11` lapping. said ends and' sealed to metal collars 12 the far margins of each of whichl are soldered or otherwise secured vacuumtig'ht to annular anges 12a, 12b encircling and sealed tio the outside cylindrical surfaces of the body .sections proximate to the facing ends of said' sect-ions; The outer or far endsrof the cylinders or body sections 10 are sealed by metallic or other headers 13. Carried by, sealed to and` projectinginwardly of the cylinders from said headers are coaxial inner cylinders 14` which extend from their respective headers toward each other but with greater spacing between the approaching ends thereof than be` tween thev proximate ends of the outer cylinders.

The chambers within the outer cylinders around and beyond the inner cylinders toward' their proximate ends are arranged to constitute cavity resonators, of which one will be herein designated the reflector resonator 15 and the other designated the cathode resonator 16 for purpose of distinguishing therebetween. The proximate ends of the two cavity resonatorsv have end walls parallel to and adjacent each other with suflicient spacing for insulative purposes. The end wall 17 of the reflector resonator is shown provided with a spiral channel 18 therein, the ends of the channel having pipes-19 con'- nectcd therewith for supply and discharge of aV cooling for said wall. Said end wall 17 has, at its center, a hole or passage 20` therethrough disposed axially of the outer cylinder and opposite the end of the inner cylinder. A foraminous or other member 21 is located across said hole or passage as' a` fixed partl of said reflector resonator end wall. Said end wall, with its hole and foraminous member accordingly has a `structure constituting it a screen grid as well as a uidcooled end wall for the resonator.

The other chamber, above described as the cathode resonator 16, has an end wall 22 at the center of which is a hole or passage 23 of corresponding size to and aligned with hole or' passage' 20f of the screen grid or reflector resonator end wall I7. It will be observed that this cathode resonator end wall 22, as well asV abovedescribed end wall 17 of the reflector resonator, and both passages 20 and 23throu'gh said walls, and` gap 24 between said walls, are all within the' evacuated interior of the tube or device.

A -directly or indirectly heated cathode within cathode resonator 25 is provided 16 in axial alignment with and `close proximity to the control grid in form of holes or vpassages 23 in end wall 22. Said cathode is carried at the inner end of a hollow core 26 located coaxially within the resonator inner cylinder 14. The cathode is electrically connected to said core which accordingly constitutes a lead-in as well as a support for the cathode. The outer en-d of the core is seated in and soldered to an end plate 27 with a vacuum-tight joint and the plate is supported at the exterior of header 13 by a glass or other insulative cylindrical band 28 sealed at its edges to oppositely projecting collars 29 respectively soldered vacuum-tight to the outwardly directed face of the header 13 and to the inwardly directed face of the end plate 27. Lead-in wires 30 for the cathode heater are introduced into the said core through the end plate 27 and With the aid of an appropriate seal 3l.

An anode 32 is provided within the anode resonator in spaced relation to screen grid 17 and coaxial therewith. Said anode is carried at the inner end of a hollow core 33 located coaxially within the resonator inner cylinder 14. The anode is electrically connected to said core which accordingly constitutes a lead-in as well as a support for `the anode. The outer end. ofthe core is seated in and soldered to an end plate 34' with a vacuum-tight joint and' the plate is supported at the exterior of header 13 by a glass or other insulative cylindrical band 35v sealed at its edges to oppositely projecting collars 36 respectively soldered vacuum-tight to the outwardly directed face of header 1'3 and to the inwardly directed' face of the end plate 34:.

Both ofV the' above-described cores 26 and 33 are providedV with chokes. 37 to prevent leakage of high frequency energy from the resonators through the respective end plates. These chokes are constructed in accordance with usual practice a quarter wavelength in dimension from a closed to an` open end, thereby presenting an effect of short circuit atr the closed end of the choke across the gap between the resonator inner cylinder and said core.

Both resonators are tunable, for which purpose each is provided with an annular piston 38 in the annular space between the outer and inner cylinders 10 and 14, the piston having. a closed end toward the inner end. of the resonator and having quarter wavelength skirts projecting from said closed endV of the piston in direction toward the header end of the cylinders. These pistons are each carried by a movable ring 39 opposite the open end of the skirt and the ring is supported by a plurality of rods 40 parallel to the cylinder axis andk projecting through the header 13. A suitable bellows or other means 40a is sealed to each rod and to the header permitting necessary sliding of the rod in the header and cylinder for tuning purposes and yet maintaining a vacuum-tight condition between the rod and header.

A' coaxial line 41 terminating as a loop 42, is introduced into the cathode resonator and constitutes a radio frequency input from a suitable source which may conveniently be a feedeback of a part of the radio'frequency energy produced in the anode resonator. The anode resonator is also shown equipped with a coaxialline 43 terminating as a loop 44 in said resonator and constituting a radio frequency output.

An external source 45 of direct current potential is provided, the electrically positive terminal of which is connected, as by wire 46 to the screen grid 17 by way of flange 12a and anode resonator outer cylinder 10. The negative' part of the source 45, with tap adjustment, is connected to the anode 32 through agency of wire 47 and core 33; Line 47 may include the secondary 48 of a transformer 49 the primary 50 of which is' connected with an audio, video-voltage, or other source of modulation.

A tap 51 to the source of'- direct current potential 45 atan intermediate part thereof, leads through a branch 52' to the flange 12b and to the cathode resonator end wall 22 which therefore functions as a grid at negative potential with respect to the screen grid 17. Another branch' 53 from said tap 51 leads through a leak resistance 54, and' grid bias 54a to the cathode 25 by way of end plate 27 and core 26. Thus the control grid is negatively biased with respect to the cathode, the cathode being on a high negative potential with respect to the screen grid, while the anode, depending on the desired modulation conditions, will have a voltage of relatively small value, positive or negative, with respect to the cathode. The cathode cavity is allowed to have a high Q, that is, a high ratio of reactance to resistance.

The screen grid 17 and reiiector 32 are constructed and arranged to form a divergent electron mirror by which the reflected electrons cannot return through the screen grid opening, which may be aided by producing an already divergent bundle of electrons through suitable lens action prior to passage through the screen. For simplicity of showing, the addition of a radial cornponent to the electron motion, is herein indicated as obtained by convex formation of the end of the reector which faces the cathode thereby setting up curved lines of electric field 55 which resolve into axially directed and grid lradially outward directed components of force of the electric field, thereby effecting a fountain-like appearance of the electron stream 56 as shown in Fig. 2. As a result, the electrons are collected over a relatively large area of the fluid-cooled screen-grid surface on their reflected trip from proximity to the reflector. From the fact that, as explained above, the reflector and screen grid have considerable spacing, it follows that in a resnatron of the present invention the reflected beam is spread over a wide area of the screen grid, and due to lower reflector-screen capacity, a relative increase in band width over prior art resnatrons is achieved.

The construction shown and above described is to be understood as illustrative and not restrictive of the features of novelty of which one is broadly the provision and operation as a reex resnatron of an electron dis- .charge device of the general type of ultra high frequency tetrode. The invention provides a reex resnatron combining the characteristics of a power amplifier with that of an absorption modulator with little or no power demand on the modulation generator shown as feeding transformer 49. Furthermore, the invention provides a radio frequency generating and modulating device which operates according to the above-discussed theory, specifically with voltages and distances related to frequency as given by the formulas herein recited, with the resulting advantage of larger distances between screen and reflector than heretofore usable in resnatrons between screen grid and prior art anode. Therefore it can be said that the reex resnatron herein shown as exemplifying the broad concept of the invention includes contributing features such as means to produce a divergent electron beam, provision of a predetermined rellatively large reector-screen distance, ample cooling and heat capacity of the screen grid, and construction and arrangement for high Q of input cavity resonator.

We claim:

1. A resnatron comprising two coaxial outer cylinders of substantially equal lengths and equal diameters having ends thereof toward each other and closely spaced, each cylinder having a piston therein directed toward and at a distance from said ends and each piston being centrally apertured, a pair of coaxial inner cylinders one in each of said outer cylinders and coaxial therewith and said inner cylinders having ends directed toward each other but with materially greater spacing from each other than the spacing of said ends of the outer cylinders, diametric walls terminating said ends of the other cylinders, each of said Walls having a central grid therein, each said inner cylinder therein and protruding at both ends thereof, a cylindrical glass band on the far ends of said inner cylinders sealed thereto at one end of each band, and means at the other end of each band sealed thereto and rigidly mounting a respective one of said cores rigidly and coaxially in said inner cylinder, a rst one of said cores providing a cathhaving a hollow coaxial core ..8 ode at its end toward the other core and the said other core providing a convex reflector at its end toward said first one of said cores, the enclosure provided by said inner and outer cylinder and between the piston and end wall thereof constituting a resonator with the said cathode in one said resonator and the reflector in the other and with the volume of the resonator enclosures substantially equal one to the other.

2. A resnatron comprising two coaxial outer cylinders of substantially equal lengths and equal diameters having ends thereof toward each other and closely spaced, each cylinder having a piston therein directed toward and at a distance from said ends and each piston being centrally apertured, a pair of coaxial inner cylinders one in each of said outer cylinders and coaxial therewith and said inner cylinders having ends directed toward each other but with materially greater spacing from each other than the spacing of said ends of the outer cylinders, diametric walls terminating said ends of the outer cylinders, each of said walls having a central grid therein, each said inner cylinder having a hollow coaxial core therein and protruding at both ends thereof, a cylindrical glass band on the far ends of said inner cylinders sealed thereto at one end of each band, and means at the other end of each band sealed thereto and rigidly mounting a respective one of said cores rigidly and coaxially in said inner cylinder, a rst one of said cores providing a cathode at its end toward the other core and the said other core providing a convex reflector at its end toward said rst one of said cores, the enclosure provided by each inner and outer cylinder and between the piston and end Wall thereof constituting a resonator with the said cathode in one said resonator and the reflector in the other and with the volume of the resonator enclosures substantially equal one to the other, and chokes on each of said cores within said inner cylinders correspondingly spaced from said ends of said inner cylinders directed toward each other.

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